Make cookies for devicemapper operations unique

Currently, the devicemapper library sets cookies to correlate wait operations,
which must be unique (as the lvm2 library doesn't detect duplicate cookies).
The current method for cookie generation is to take the address of a cookie
variable.  However, because the variable is declared on the stack, execution
patterns can lead to the cookie variable being declared at the same stack
location, which results in a high likelyhood of duplicate cookie use, which in
turn can lead to various odd lvm behaviors, which can be hard to track down
(object use before create, duplicate completions, etc).  Lets guarantee that the
cookie we generate is unique by declaring it on the heap instead.  This
guarantees that the address of the variable won't be reused until such time as
the UdevWait operation completes, and drops its reference to it, at which time
the gc can reclaim it.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>

pkg/devicemapper/devmapper.go

@@ -328,11 +328,11 @@ func RemoveDevice(name string) error {
 		return err
 	}
 
-	var cookie uint
-	if err := task.setCookie(&cookie, 0); err != nil {
+	cookie := new(uint)
+	if err := task.setCookie(cookie, 0); err != nil {
 		return fmt.Errorf("devicemapper: Can not set cookie: %s", err)
 	}
-	defer UdevWait(&cookie)
+	defer UdevWait(cookie)
 
 	dmSawBusy = false // reset before the task is run
 	if err = task.run(); err != nil {
@@ -361,10 +361,10 @@ func RemoveDeviceDeferred(name string) error {
 	// set a task cookie and disable library fallback, or else libdevmapper will
 	// disable udev dm rules and delete the symlink under /dev/mapper by itself,
 	// even if the removal is deferred by the kernel.
-	var cookie uint
+	cookie := new(uint)
 	var flags uint16
 	flags = DmUdevDisableLibraryFallback
-	if err := task.setCookie(&cookie, flags); err != nil {
+	if err := task.setCookie(cookie, flags); err != nil {
 		return fmt.Errorf("devicemapper: Can not set cookie: %s", err)
 	}
 
@@ -377,7 +377,7 @@ func RemoveDeviceDeferred(name string) error {
 	// this call will not wait for the deferred removal's final executing, since no
 	// udev event will be generated, and the semaphore's value will not be incremented
 	// by udev, what UdevWait is just cleaning up the semaphore.
-	defer UdevWait(&cookie)
+	defer UdevWait(cookie)
 
 	if err = task.run(); err != nil {
 		return fmt.Errorf("devicemapper: Error running RemoveDeviceDeferred %s", err)
@@ -471,13 +471,13 @@ func CreatePool(poolName string, dataFile, metadataFile *os.File, poolBlockSize
 		return fmt.Errorf("devicemapper: Can't add target %s", err)
 	}
 
-	var cookie uint
+	cookie := new(uint)
 	var flags uint16
 	flags = DmUdevDisableSubsystemRulesFlag | DmUdevDisableDiskRulesFlag | DmUdevDisableOtherRulesFlag
-	if err := task.setCookie(&cookie, flags); err != nil {
+	if err := task.setCookie(cookie, flags); err != nil {
 		return fmt.Errorf("devicemapper: Can't set cookie %s", err)
 	}
-	defer UdevWait(&cookie)
+	defer UdevWait(cookie)
 
 	if err := task.run(); err != nil {
 		return fmt.Errorf("devicemapper: Error running deviceCreate (CreatePool) %s", err)
@@ -659,11 +659,11 @@ func ResumeDevice(name string) error {
 		return err
 	}
 
-	var cookie uint
-	if err := task.setCookie(&cookie, 0); err != nil {
+	cookie := new(uint)
+	if err := task.setCookie(cookie, 0); err != nil {
 		return fmt.Errorf("devicemapper: Can't set cookie %s", err)
 	}
-	defer UdevWait(&cookie)
+	defer UdevWait(cookie)
 
 	if err := task.run(); err != nil {
 		return fmt.Errorf("devicemapper: Error running deviceResume %s", err)
@@ -757,12 +757,12 @@ func activateDevice(poolName string, name string, deviceID int, size uint64, ext
 		return fmt.Errorf("devicemapper: Can't add node %s", err)
 	}
 
-	var cookie uint
-	if err := task.setCookie(&cookie, 0); err != nil {
+	cookie := new(uint)
+	if err := task.setCookie(cookie, 0); err != nil {
 		return fmt.Errorf("devicemapper: Can't set cookie %s", err)
 	}
 
-	defer UdevWait(&cookie)
+	defer UdevWait(cookie)
 
 	if err := task.run(); err != nil {
 		return fmt.Errorf("devicemapper: Error running deviceCreate (ActivateDevice) %s", err)